An Isolable 2,5‐Disila‐3,4‐Diphosphapyrrole and a Conjugated Si=P−Si=P−Si=N Chain Through Degradation of White Phosphorus with a N,N‐Bis(Silylenyl)Aniline

Abstract White phosphorus (P4) undergoes degradation to P2 moieties if exposed to the new N,N‐bis(silylenyl)aniline PhNSi 2 1 (Si=Si[N(tBu)]2CPh), furnishing the first isolable 2,5‐disila‐3,4‐diphosphapyrrole 2 and the two novel functionalized Si=P doubly bonded compounds 3 and 4. The pathways for the transformation of the non‐aromatic 2,5‐disila‐3,4‐diphosphapyrrole PhNSi 2P2 2 into 3 and 4 could be uncovered. It became evident that 2 reacts readily with both reactants P4 and 1 to afford either the polycyclic Si=P‐containing product [PhNSi 2P2]2P2 3 or the unprecedented conjugated Si=P−Si=P−Si=NPh chain‐containing compound 4, depending on the employed molar ratio of 1 and P4 as well as the reaction conditions. Compounds 3 and 4 can be converted into each other by reactions with 1 and P4, respectively. All new compounds 1–4 were unequivocally characterized including by single‐crystal X‐ray diffraction analysis. In addition, the electronic structures of 2–4 were established by Density Functional Theory (DFT) calculations.


A1. General considerations
All experiments and manipulations were carried out under dry nitrogen using standard Schlenk techniques or in an MBraun inert atmosphere dry box containing an atmosphere of purified N2.
Solvents were deoxygenated and dried by standard methods, saturated with purified N2 and freshly distilled prior to use. The precursor compounds PhNLi2 1 and PhC[(tBu)N]2SiCl 2 were prepared according to literature procedure. The 1 H, 13 C, 31 P, 29 Si-NMR spectra were recorded on Brucker AV200, AV400, AV500 spectrometers referenced to residual solvent signals as internal standards ( 1 H NMR: C6D6, 7.16 ppm; THF-d8, 1.76 and 3.62 ppm; 13       Compound 3: 50 mL Et2O was added to a mixture of 1 (0.91 g, 1.49 mmol) and P4 (0.14 g, 1.14 mmol) at room temperature. After the reaction mixture was stirred overnight, the volatiles were removed under vacuum and the residue was washed with n-hexane (25 mL), yielding 0.77 g (0.55 mmol, 74% yield) of 3 as orange crystals. The X-ray analysis qualified crystals were

Reactivity of 3 toward (Xant)Si2:
Reaction of 3 with (Xant)Si2 to give 2 and B: 0.50 mL d8-THF was added to a mixture of 3 (0.0032 g, 0.023 mmol) and (Xant)Si2 (0.0066g, 0.0090 mmol) in an NMR tube at room temperature. After three days the 31 P{ 1 H} NMR spectrum of the resulting mixture exhibited a signal at δ = -282.4 ppm for B and a signal at δ = -328.0 ppm for 2 ( Figure S19).

Reactivity of 4 toward P4:
d8-THF (0.50 mL) was added to an NMR tube with 4 (0.0110 g, 0.0085 mmol) and P4 (0.0010 g, 0.0081 mmol) at room temperature. The 31 P{ 1 H} NMR spectrum of the reaction mixture showed that compound 4 converted to 3.       Figure S22. Molecular structure of for 3. Thermal ellipsoids are drawn at 50% probability level.

A4. Details of the single crystal X-ray diffraction analyses
Hydrogen atoms are omitted for clarity.  Figure S23. Molecular structure of for 4. Thermal ellipsoids are drawn at 50% probability level.
Hydrogen atoms are omitted for clarity.

B Computational Section
Computational details. All the calculations were performed using the Gaussian 16 software package. 4 Geometry optimization of the compounds was conducted at the TPSS-D3BJ 5 density functional theory level, according to the best agreement with the metric data from X-ray structure analyses (Table S9, S10, S11). The Def2-SVP 6 basis set is used to describe C, N, H atoms, whereas ma-TZVP 7-8 basis set is used to Si and P atoms. In addition, frequency calculations are carried out at the same level of theory to confirm the stationary points are minima with no imaginary frequencies. Furthermore, the B97-2 9 /Def2-TZVP 10 method is used to calculate the 31 P NMR chemical shifts, where the solvent effect (solvent = THF) is taken into account by SMD model. The calculated 31 P absolute shielding constants are converted to 31 P NMR chemical shifts, with 85% water solution of H3PO4 as reference. Here, we use σ(H3PO4) = 328.35 ppm suggested by Jameson et al. 11 The calculated 29 Si absolute shielding constants are converted to 29 Si NMR chemical shifts, with that of tetramethylsilane (TMS) calculated at the same level (σ(TMS) = 338.2 ppm) as reference. Viewing of optimized structures and rendering of molecular orbitals were performed using the program CYLview 12 and VMD, 13 respectively. NMR spectra were drawn in the Multiwfn program. 14 EDDB and NICS calculations were performed at the CAM-B3LYP/def2-TZVP level.
Here, the more representative NICS(1)ZZ was employed to aromaticity calculation because it has been proven as a good index for both the S0 and T1 states. 15 Since the 6/5MR in compounds D and 2 are nonplanar, their NICS(1)ZZ values are averaged at 1Å above and below the ring center. For TD-DFT, PBE0 is used for UV/vis absorption simulation calculation at gas phase because König et al. 16 indicates that PBE0 performs well in the calculation of excitation energy. NMR analysis. According to the DFT calculation, the peak located at -340.1 (σexp. = -330 ppm of 2) is assigned to the P1 and P2 atoms ( Figure S24).     The calculation of UV absorption spectrum. According to the DFT calculation, the maximum absorption wavelength located at 600.2 nm (λexp. = 568 nm) of 2 ( Figure S29), and the oscillator strength (f) is 0.0361. The HOMO was mainly localized on the five-membered ring moiety, whereas the LUMO was mostly localized on the benzene rings of the both side ( Figure S28). The computed absorption band (λ = 600.2) can be assigned to the electronic transitions HOMO→LUMO+2 (19.2%), HOMO→LUMO+5 (72.2%). In addition, we also located an absorption peak at 421.2 nm (λexp. = 426 nm) with f = 0.0151, and the computed absorption band can be assigned to the electronic transition HOMO-1→LUMO (77.8%).